Position-adjusting mechanism



C. E. CUSHMAN POSITION-ADJUSTING MECHANISM Dec. 18, 1951 Filed Jan. 26, 1948 5 Sheets-Sheet 1 L5 INVENTOR.

tun-020E C'l/JHMAN c. E. CUSHMAN 2,579,305

POSITION-ADJUSTING MECHANISM 5 Sheets-Sheet 2 w //I l Dec 18, 1951 Filed Jan. 26, 1948 AGENZ' Dec. 18,1951 c. E. CUQHMAN POSITION-ADJUSTING MECHANISM 5 Sheets-$heet 4 Filed Jan. 26, 1948 m l. I

\\\\\\\\\\ \\\V/// //lll /////ll/l/ INVENTOE Q CUP-F020 EC'USHMAA/ AGENT:

c. E. USHMAN POSITION-ADJUSTING MECHANISM" Dec. 18, 1951 5 Sheets-Sheet 5 Filed Jan. 26, 1948 kw as Q s INVENTOR. Q #7020 5- C'USHMAN BY AGENE Patented Dec. 18, 1951 fosmofi-Afiins'rme} MECHAfiiSM aunt e E1 cushmen, Burbank, C l a, assigner t stilige'ss Inc.,- a corpdfiififin of 'Galifo'lnia' Afiiiiiation January 26, 1M8, serial No. 4,347"

(oi. m ne) This ih'vehti' 'n reiates to adjustable rheha'rii'cal structures and artie afli? to improved posh tion 'adjiisting iheehf The inventio hossessespai'tieular' iitilitif in ceiiiieeti'on with rej-- clining chairs having tiltable Hacks and for this uai eehtrei at the chair eeetip ht in order to a permit relative mov ment-"iii th frictional mem reason is deseiihedih detail in connection the'iewith, sithei eh-the hventish is described with particular reference ts seen chairs, it is to he iihdeisteed that man of its features are appii= cable in connection with other mechanical Strut: titres comprising heirs of relatively movable intereehheetea stiueturei members, such as pairs of pivoted members. A w

(A, positiomadjus'tifig' mechanism of thetyiie' to which this invention is'p'ait'ieiflai'm directed includes a braking mechanism including a hair '61: v 'f rictionally ehgaseame holdin ,r'r"1eff1bers which arerespeetivew mounted eh or otherwise connected to two such relatively movable strutstt'iraI members, In paftiiilai; for eiia'i'xi 1t'; an adjustable reclining chaii" Of the type which is employed on airplanes and to which this'i vention is especially applicable includes three" chaif' members, namely: a s pport member, a seat member; and e tiltahie back member, oi" their back. Such a support member is figidli inoiinted en the near ofan airplane and the seat ember in many instances issiidahly eat rise by the siihport meihheriii 's'iic'h a' way' 'that it can move backward and roman; there-eh, and the back member" is .bive'tany attached to' the semen memb r she also attached te the seat member in such a way that; as the hack" iiieihher is tilted backward and forward" with resheette the suppert member; the seat member is also earned backward and forwarjd into correspond: ingpositions, Adjusting mechanisms of the type with which this invention is'conceifnd are coniieetea betweeiiany two of such relatively ifimi= able members iii sueh a way as" to hole thejiii securely together thereby making" the chaiif in" some predetermi ed Shape to Siiit the comfort of the occupant; The adjustment ef fueh a chair is preferably ufidef' the eeiitiel of the t eir steepest, the adjustment heiiie. acoiiiplished most eei veiiiehtiy by means of a eo'ntnil member mounted at the side of the chair, such as on the their arm. 4

The type of position-adjusting'ifichanisiii to tvhieh this invention is rimarily tii 'eeted'eoinprises apair of frictiohany ehgageahle mehihers or groups or memherswhieh sari/e as a hrake for locking the chair inenihers in ant selected i-eiative positions. "Tiie' frictidiially engageebie members forth a atter a friptidn type' locking devicewhich prefers-51y includes shit-able 'i'iieaiis' fer i-eieasiiie the Bfakin iiirr'ibeis under thanhers in eithendirection. With this arrangement, it is re ttiveiy easy te release the brake and adjust the shape at t e chair by mo ing the hair member's 'r'eiative1y between predetermined extreme positions. n h p v Usu l y a series at ehairs employing su'ch esif16fi=adjusting mechanisms is arranged seriatim, one behihda et i, such as in the eabin of an stable to pef'n'iit the mtki e device on one of thefiehairs ta be re1eased' rea ily a force is'ah iied to the chair in an opposite direction. For example, if one chair is vacant and the oc= ee'paht th chaii' behind w shes to rise, it is often desirable that he'he able to push or tilt the back-0f the ehair immediately receding hintierwermy' into a more upright position, in order to give him more teem for rising, Also, of eeiirsewheii a chair is unoccupied, it is often desfr hie to ifio've' the chair-back to the upright position for" the maxim m ofivenien'c'e' of the occupant of the ehaii Behind.

In the opendine patent application Serial No. 1 864 filed Januarir i2, 1948, now abandoned, there has bend'scribed and claimed a p-ositiom adjusting mechanism which comprises a pair of coniplen ehtarily threaded menibers such as a nut and a screw, which is adapted to be oompressed and extended by means of axial forces a plied therebetween. The two threaded mem hers are connected between two relatively mov able structural members and can be arranged to be loeked 'in any desired position by means of a brake shoe; which is adapted to frictionally engage a brake drum on the periphery of the nut; The present invention is applicable to that type of position-adjusting mechanism as well as to others in which irictionally engageable brake members are employed for. locking the mach ani'sm in a predetermined position, as more fully described hereinaftery s (D'ne of the otijects of the invention is to pro vide an adjustable chair with an adjustable p'osi ti'oniii'g' deviee employing fric'tion'aily ehg'ageame braking" suriaees' with for holding the backmember or the email agaiiist'iel'atiiil y large ieafwa-fd =tiltin forces but which permits the back member to he moved forward-tilting forces exeeeehie'ait'eIatiVeIt low predetermined tame.

posing forces applied in one direction betweenopposite direction.

said members and with means .which causes slippage of said braking surfaces when such force exceeds a predetermined value.

Another object of the invention is to-provide an adjustable positioning mechanism employing a braking mechanism having frictionally engageable braking surfaces with means including a spring for urgin said braking surfaces together to resist relative movement thereof by forces applied in one direction and means coopcrating with the spring for maintaining the frictional force between said braking surfaces substantially constant independently of the coeflicient of friction therebetween so that the positioning mechanism may be adjusted whenlsuch H forces exceed a substantially constant predetermined value. 7

Another object of the invention is to provide a position-adjusting mechanism with a preloaded spring which opposes adjustment forces in a predetermined direction and which urges frictionally engageable braking surfaces together to produce frictional forces which resist such adjustment forces.

4 reclining chairs, it is to be understood that it is also applicable to other types of structures in which it is desired to provide a locking device which holds against relatively large forces in one direction and relatively small forces in the The foregoing and other advantages, objects, and features of the invention" which distin'guishit. from the prior art, will be readily apparent from a consideration of the several embodiments of the invention which are illustrated in the accompanying drawing and the following description thereof.

In the drawings, wherein the same numbers in the several views represent like parts:

Figure 1 is a partly broken away isometric view of an airplane chair incorporatin the invention;

Fig. 2 is a fragmentary view showing the control button mounted on the chair arm;

Fig. 3 is a side elevational view of a first form of the improved position- -adjusting mechanism;

Fig/4 is a fragmentary sectionalview of the first position-adjustingmechanism taken on the plane44ofFig.6; V

Fig. 5 is a longitudinal sectional view of the first position-adjusting mechanism of Fig. 1;

Fig. 6 is a view of the firstposition-adjusting mechanism of Fig. 1 taken on the plane 6-6 of Fig. 3;

Fig. '7 is a detailed sectional view of. the first position-adjusting mechanism taken on the plane 1-1 of Fig. 3;

Fig. .8 is a detail view of the brake mechanism of the first position-adjusting mechanism taken Another object of the invention is to provide 3,

a position-adjusting mechanism which employs such a preloaded spring with means for adjusting ably varying the'value of the force which must be exceeded to cause adjusting of the mechanism.

Another object of the invention is to provide such a position-adjusting mechanism which is of simple low cost light weight construction, which operates'silently and reliably;

According to the'present'invention, a frictiontype locking device is provided with'means for M holding the pair of frictionally engage'able elements together in braking, or locking, engagement for a large range of forces applied in a forward direction to the top of the chair-back,

but only for a small range offorces applied in the opposite direction. With this arrangement,

the locking device is adapted to hold a chair locked in a predetermined shape against the weight of its occupant or any similar force which tends to tilt the chair back-rearwardly, but at the same time,-is adapted to permit the'chairback to be tilted upwardly, or forwardly, into an erect position by means of a relatively small forwardly directed force.

More particularly, in accordance with this invention, sucha locking device is provided with described in connection with its application to on the plane 8-8 of Fig. 7;

Fig. 9 is a longitudinal sectional view of a second form of the position-adjusting mechamsm;

Fig. 10 is a sectional view taken on the plane Ill-l0. of Fig. 15 showing'details of the braking mechanism of the second form of the positionadjusting mechanism;

Fig. 11 is an exploded isometric view of the braking device of the second form of the positionadjusting mechanism;

Fig. 12 is a side elevational view of a third form of the position-adjusting mechanism;

Fig. 13 is a longitudinal sectional view of the third form of the position-adjusting mechanism taken on the plane l3-l3 of Fig. 12;

Fig. 14 is a detailed sectional view of the third form of the position-adjusting mechanism taken on the plane [4- 44 of Fig. 13; I

Fig. 15 is an isometric exploded View of the brake lever of the third form of the position-adlusting mechanism;

1 20-20 of Fig. 19 showing details of the braking mechanism of the fourth form of the position-adjusting mechanism;

Fig. 21 is a detail view taken'on the plane t 21-2l of Fig. 19, also showing details of the last While the invention is particularly shownand mentioned braking mechanism; and

Fig. 22 is a fragmentary view of a canting leaf employed as a braking member of the last m'en tinned braking mechanism.

" PART I Introduction In the drawings, there are illustrated four forms of position-adjusting mechanism incorporating the features of the present invention as applied to a reclining airplane chair. Each of-these position-adjusting mechanisms comprises a housing or body member and a rod member longitudinally movable therein. These two members are connected respectively to two of the relatively movable structural members of the airplane chair or other articulated structure which is to be ad- Justably set in predetermined positions. Each of these position-adjusting mechanisms is. M ranged to be extended, or expanded, and to be compressed, or contracted, in response to axial forces applied between the body member. and the rod member. Each of the position-adjusting mechanisms includes a braking mechanism which comprises two frlctionally engageable braking members which are adapted to hold or lock the position-adjusting mechanism in any pre-set position when they are engaged. In practice, a brake-release mechanism is provided for disenfgaging the braking members to release the brake mechanism in order to accomplish the desired extension and compression from one predetermined position to another. In practice, as applied to a reclining chair in the embodiments of the in vention illustrated,- each of the position-adjusting mechanisms'is compressed when the back member of. the chair is tilted backwardly and is extended when the back member is raised to its upright position. A backwardly directed force may be applied to the top of the chair-back to effect the compression and a forwardly directed force to effect the extension. For convenience they are referred to herein as compression and extension forces respectively.

The three forms of the invention illustrated in Figs. 1 to 1'7 inclusive, are of the type covered by the aforesaid copending patent application in which the braking mechanism comprises one brake member, or one group of brake members, mounted on the body member and another brake member, or group of brake members, mounted on the rod member. In this type of the lnven tion, the rod member is in the form of a threaded screw and the brake member, which is mounted thereon, is rotated relative to the body member by means of a threaded nut which engages the threaded rod. In another type of the invention illustrated in Figs. 18 to 21 inclusive, the first brake member or group of brake members, is also I mounted on the body member, but the second brake member is provided by the surface of the rod member itself. In all forms of the invention, the first and, second brake members are normally urged together into frictional'engagement to lock thefpositiomadjusting mechanism in any set position and the brake members may be disengaged by means of a brake-release mech anism controllable from" the arm Got the chair to which the position-adjusting mechanism is ap-' plied. In addition, means such as an overload spring is provided in each form of the invention for maintaining the-brake members engaged as long as any compression force is less than a predetermined relatively large value. Also, in

' addition, means such as an overridespring provided in'eacn form of the invention for maintainlng'the members engaged as long as'any'ex tension force is. less than a predetermined rela tively small value.

Before considering the details of construction of the two types of position=adjusting mecha nisms illustrated, it is first desirable to consider the structure of an airplane chair I0. in connection with which each of these.-positiomadjusa ing mechanisms is used. I The chair In comprises a support member l2", a seat member Idand a tiltable back member IS. The support member I2 comprises two internallybraced side member I8 having feet at by means of which the chair It is secured to the floor or an airplane and having arms, or arm-rests, 2| for the comfort of the chair occupant. Thesup port-member I2 alsoincludes a front cross-bar or cross rod 22' interconnecting the side member's I8 just below seat height. The back member it, which carries a back cushion. is pivotally at: tached to'the rear portion of'side members I 8 by means of brackets 24 attached to opposite sides of the back member and pins 26 rojecting in wardly from the back ends of the arms 2|. The pivotal interconnections between the support member I2 and the back member I6 serve to fur ther strengthen the chair I0. I The seat member I4 comp ises a seat frame 25 which bears a seat cushion 20. The back end of'the seat is-pivot'ally supported by pins 2'! on the lowermost end or the back member I6 and-its front-end is slidably supported on the frontcross bar 22 by means of slotted guides 25 extending downwardly from the seat frame and pins 30 carried by lugs .32 extending upwardly from the front: cross-bar. A rear cross-bar '34 is attached to opposite sides of the back member I6 atthe bottom end thereof beneath the pivot pins 21. I

Each of the four position-adjusting inecha= nisms incorporating the present invention and hereinafter designated by the'numer'als I00, 200, 300, and 400, is preferably mounted beneath the seat member I4 ininterconnecting relationship between the two cross-bars 22 and 34 andmid way between the two side members I8. Each of these position-adjusting mechanisms: is locked and unlocked by manipulationv of a control member in the form of abutton 42 mountedv at the front end of one of the chair arms 2I. While the position-adjusting mechanism is thus unlocked, permitting it to be extended or compressed,

the back member II; may be readily moved by the chair occupant from one tilted. position to another. But while the position-adjusting mechanism is locked, the back member I6 is held firmly in the tilted position selected.

PART II Screw type Form 1.The-first position-adjusting mechanism I00 comprises a divided housing member I02 and a rod member I04 which are respectively pivotally mounted on the two cross-bars 22 and 34. The housing member I02 is held together by means of screws I03. The rod member I04 carries a threaded nut H36 which is mounted for rotation in the housing I02 by means of front and rear balk-bearing assemblies I08 and I09 at opposite ends thereof. Both the rod member Illdand the nut I 05 are provided with multiple-start threads. Rotation of the nut I06 in the housing I02 is preventedby means of a braking mechanism H0 including a stator 'memher in the form of-a segmental conical brake shoe II2 which mates with and friction'ally' engages a rotor member in the form of a conical brake drum I I4 arranged on the periphery of the nut. The brake shoe 2 and the brake drum II4 are tapered forwardly, the former being suitably made of Micarta and the latter aluminum.

When the braking mechanism is engaged, the position-adjusting mechanism I is locked against extension and compression as long as the extension and compression forces lie below corresponding limits as more fully explained hereinbelow.

It is to be noted that the housing I02 carries trunnions I20 at opposite sides thereof by means of which it is supported on a universal coupling 64 which is pivotally attached to a front bracket 68 extending rearwardly fromthe front cross-rod 22, and that the rod member I04 is pivotally connected to the rear cross-rod 34 by means of a rear bracket 56 extending forwardly therefrom. Furthermore, it is to be noted that the working parts of the position-adjusting mechanism I00 are arranged within a dust-proof housing including the housing member I02, a forwardly-extend- I ing tube I30, and a collapsible tubular member I32 in the form of a Sylphon bellows. The threaded rod I04 is arranged to be longitudinally movable in the housing I02 through concentric front and rear openings I36 and I38 at the front and rear ends respectively of the housing member I02. These and many other details of construction are described more fully in the aforesaid copending patent application.

The inner races I40 and MI of the ball-bearing assemblies I08 and I09 abut front and rear shoulders I42 and I43 at opposite ends of a central collar I44 of the nut I06. The outer races I46 and I41 of the ball-bearing assemblies I08 and I09 slidably engage the cylindrical Wall of the main cavity I48 which extends longitudinally within the housing member I02 in coaxial relationship with the openings I36 and I38. The front outer race I46 normally engages the inner surface of the wall portion I49 surrounding the front opening I36. However, the rear outer race is free to move within the space at the rear end of the cylindrical cavity I48.

The nut I06 and the ball-bearing assemblies I08 and I09 are normally urged forwardly within the cavity I48 by means of a preloaded push- I I2 is exerted against the drum II4 by means of a crank I60 including an eccentric cylindrical crank rod I62 supported between a crank hub I64 and a crank pin I66 both of which are journalled-in facing walls of a portion of the housing member I02 as illustrated in Figs. '7 and 8. The crank rod I62 rests within a send-cylindrical cross-slot I68 on the side of the brake shoe II2 oppositethe conical braking surface I58 thereof. 7

A crankarm I is welded to the crank hub I64 andextends radially therefrom in the same direction in which the crank, rod ,l 62 1is offset:

from the center of the crank I80. The crank arm I10 stands adjacent to the periphery of the housing member I02 and its outer end I14 is drawn toward the housing member by means of a coiled tension spring I16.

The inward movement of the crank arm I10 toward the housing member I02 is limited by means of a stop screw or stop pin I18 projecting radially therefrom. This stop pin or stop screw I1 8 extends radially inwardly toward the housing member I02 and is adjustable radially-in a threaded female part I19 welded to the crank arm I18 and is locked in any desired position by means of a holding nut I80. Preferably the inner end of the stop pin is spaced slightly from the outer surface I8I of the wall of the housing member I02 when the brake shoe II2 engages the brake drum H4 in the most forward position of the threaded nut I06 in the housing I02 and engages the housing member I02 firmly when the nut I06 is drawn rearwardly in the housing member I02 against the force, of the override spring I50.

Thus, with this arrangement, a substantiallyv constant pressure is exerted by the brake shoe II2 against the brake drum II4 while engaged, irrespective of the axial position of the threaded nut I06 in the housing I02 so long as the pin I18 is spaced from the surface NH. The brake shoe II2 may be withdrawn from the brake drum II4 by -means of a flexible cable or wire such as a Bowden wire 86 which is controllable by means of the release button 42 mounted on one of the chair arms 2| as more fullyset forth in the aforesaid copending patent application to permit the chair-back l6 to be raised and lowered.

In said copending patent application, it has been explained how a position-adjusting mechanism of the type described above is capable of supporting large axial loads by means of a small force exerted by an overload spring I16 provided that the pitch angle a of the threads of the rod I04 and the nut I06 is only slightly greater than the binding angle. The binding angle is the minimum pitch angle a at which the nut I06 would be locked against rotation on the rod I04 when an axial thrust is applied therebetween, while the nut is constrained against axial movement in the housing I02. The binding angle depends upon the coefficient of friction of the threads and also upon the angle 5 between the faces of the threads. As pointed out in said application, the binding angle is approximately for dry metal-to-metal bearing surfaces. The actual mechanical advantage of such an arrangement, that is, the value of the load which may be held, divided by the force exerted by the holding or overload spring I16 is approximately inversely proportional to the deviation of the actual pitch angle from the binding angle. For this reason, in practice, the pitch angle is set at about one or two degrees greater than the binding angle, and the threads are maintained substantially dry so that the binding angle and hence the mechanical advantage of the mechanism are maintained at a high constant value. I

The actual force that must be exerted by the brake shoe II2 on the brake drum II4 to hold against a predetermined load is inversely proportional to the coefficient of friction ,u between the two frictionally -engageable members. other words, the maximum compression load eels e el es 1a the. le ieiiiee ecuat en e Y 1;) where Y Fe'maxinium compression load friction of brake shoe on brake #=T v t 9i drum, F1=tension exerted by overload spring,

Ki=constant depending on the following factors:

a t eaine ag e t e, pitc ehele meehani ai ad a tag Qt ste i value of the spring fOICG Fl is set at a value which will hold against'the desired maximum compression load for the smallest expected value I of t likely to occur under operating conditions. As a matter of fact, it is noted that-with the arrangement described, the nut I06 is constrained against any' substantial axial movement in the housing member H32- when compression thrusts I are applied. Aslong as the axial load in this direction is less than the maximum load that can be held by the overloadlspring. I16 as determined by Equation 1 the positioneadjusting device re.- n'iains securely locked. But on thevother-hand,

it is noted that the nut IDS-is free to. move'axially iii-the opposite direction against the force of the push-up or override spring. 150 when an extension thrust is applied between the rod member I05 and the -housing member I02. lif such a force is applied whiie the brake mechanism H0 is disengaged, the rearward movement of the nut is very slightand extension occurs.

But when an extension force is applied while the brake mechanism ,I ll! is en a ed, the nut IE5 is moved rearwar ly Within the hous n l0? against the f rc of he nutshzupse es i511..- u in the in ial por ion of th s movement, that s. while th extens on fo ce s sma l he brak I 10 rema s f y e sed- Ho e hen the c ank rm "9 s. ov d nward to he mint where 7:

the st p H8 cont ets th s rface. 3!. the pre sure of the brake H4 bec m s r ieve Ap ther e tee ieii fe eee-in ep eeiti e s the f .f 1, s ring i fiele eeeeestbe aetua. ve ap l d to h ake dr m H by th ev rieeei exerted between the braking surfaces fal ls heio w the al equi d te held a a ns the extension 39m. a de m ed b E ua on beve- When thi ee ure, h ne 105 a e e e-the th eaded rogl me her I04.

I to be ee edet his ant hat as see ee ee et enei t e mi ee eom'm neee, iu he r ar: were mei'fim n 9i h nut in the th ne "1? s re d the iiit bein re ili ntl e d a ainst z urthe me eieeiit- 'a'i'eeiili, iii e enee emeritei t e two brake member "2 end H is mainta ne e nu -es ate e d e tiie ier epi fa hers; tine the elee ees In practice," since the value of; e varies with age and use of the brake mechanism, the

1&0 s IQIIlQd by the overr de rin 5lt i eeeerde with; the ma nitude of the extensi n fie ce- If st ll la er ex en on tome ar a p e peci ll i t ey are. a plied s dd n yhe. nut 11 ay. e. ree rearwarcl o, the int W ere the brakev rum, U4. becomes com etel disen a ed from he br ke hoe H and. even th u h the nu "36 c ele ates the ak n meeiia ism. Hi! may r main isen ged ter a subst ntial: eriod. so on a suc a lar e e tension or e applied. 1

It s to; e n ed hat. t e ma n tude f; the ex.- tension force which is required to permit the cree rm I"! to movei iwen i to. e. point Where the etch, i Hi1 eentaie 31. .9 eu ieee it is determi ed hi? the eemnliei ee or rate tee er, 1". t e o e de. e es I 0, and th aet el degree Qi ee'ni re iqli 9f t e everrie e sprin 1511 between the 11 1i {5 enei the rear ei r 1 .5,.- Time the. meenit iie 91- the fie e ext n i n. required. t cause extension of the position-adusti l ae eia iii e ereximet t9. h i0. e. e si ed b ih irel eeed Weir series 459 e t e ot race; 4.51

1 feet t c n be hew; h e-t e a ue Q t ext i qn' 9 e ee i d is rele e he lish ub tan ia y in e enden 9? t e weffi ciem 9f fri t n aiii e1i twe.en t e akin ex ed b he wee s ti g a, If he te tenem nt d t to me 1? oi th ser ate is! s an; t i eieer xi o he ever,

r1 ie eis ncr ased u t e the esee h s r ace it" the eb Where Fs=residuai braking force just sufficient i; hold nut locked against rotation caused'by le suflicient to permit maintenance of the residual braking force just below the holding value FE.

It is to be noted that if the coefficient of friction changes for some reason even by a large amount, only a slight change in the extension force is required to establish the residual braking force below the holding value. In other words, the force required to extend the position-adjusting mechanism I is practically independent of the'coefiicient of friction a between the braking surfaces of the brake shoe H2 and the brake drum II4.

With the arrangement described, it is clear that by suitable selection of physical constants of the apparatus, the position-adjusting mechanism I00 may be readily designed to hold against compression forces up to a relatively large overload value and still permit extension when forces exceeding a relatively small value are applied in the opposite direction.

It is to be noted that the extreme positions to which the seat member I4 and the back member I6 of the chair may be moved relative to the support member I2 is determined by the stroke of the rod member I04 relative to the housing member I02. The length of this stroke is determined by the stop screw I90 at the forward end of the rod member I04 and the length of the stop sleeve I92 which is positioned between the nut I06 and the bonnet I94 within which the back end of the rod member I04 is supported.

Form 2.-A second form of the position-adjusting mechanism 200 of this invention which may be employed for adjusting the shape of the chair I0 is illustrated in detail in Figs. 9 to 11 inclusive. This position-adjusting mechanism 200 likewise comprises a divided member 202 and a threaded rod member 204 which are supported between the two cross-rods 22 and 34 of the chair in the manner hereinbefore described. In this case, a threaded nut 206 which engages the threaded rod 204 is constrained for limited axial movement within the housing member 202 between thrust-bearing assemblies 208 which are firmly secured therein by means of locking rings 2I0 which engage the outer races '2I2 of the ballbearing assemblies. The inner races 2I4 of the ball-bearing assemblies abut opposite ends of an enlarged rectangular portion 2I6 of the nut 206 in order to limit the axial movement of the nut in the housing of the two bearing assemblies. A flange 2I8 extends outwardly from the nut 206 between the ends of the rectangular portion 216 to provide shoulders to accept the thrust of sections of the braking mechanism 220 which is employed in this form of the invention to lock the position-adjusting mechanism 200 against compression and extension.

The braking mechanism 220 of this positionadjusting mechanism 200 includes a front section 222 and a rear section 224, the front section 222 being arranged on the front side of the flange M8 and the rear section being arranged on the rear side of the flange 2I8. The two sections 222 and 224 of the braking mechanism 220 are of similar construction, the details of the rear section 224 being illustrated best in the exploded view of Fig. 11.

The rear section 224 of the braking mechanism comprises a pair of rear rectangular stator discs, leaves, or plates 226 which are provided with central apertures 228which encircle the nut 206 and which are held against substantial rotation within the housing member 202 by virtue of their loose fit therewithin. The rear section 224 also includes a group of rear rotor discs, leaves, 'or plates 232 and a rear spacer 234. One of the rear rotor discs 232 is arranged between the forward stator disc 226 and the flange 2l8. A pair of the rear rotor discs 232 are arranged adjacent the facing surfaces of the two rear stator leaves 226 and the rear spacer 235 is located-between this pair of rotor discs. All three rear rotor leaves 232 and the rear spacer 234 are provided with rectangular apertures which register with the rectangular portion 2 I 6 of the nut, so that the rotor discs and the spacer 234 rotate with the nut 206 but are free to move longitudinally thereon. The front section 222 of the braking mechanism 220 comprises front stator discs, leaves, or plates 236 and front rotor discs 242 and afront rotor spacer'244 similarly arranged on the front side of the flange 2I8.

Front and rear brake levers 248 and 250 are provided for urging the stator leaves and the rotor leaves of the respective sections 222 and 224 of the braking mechanism 220 into frictional engagement. The two levers 248 and 250 extend crosswise within the housing member 202 and are provided with central openings 252 and 254 whichencircle the nut 206 at the outer ends of the stacks of stator and rotor leaves of the two sections 222 and 224; The broad ends of the two levers 248 and 250 abut two reentrant fingers 256 and 258, being urged thereagainst by a coil spring 258 in order to form pivots for the levers. The spring 258 extends through slots 26I in the ends of the stator leaves 226 and 236. Opposite ends of the spring 228 rest within recesses 260 and 262'in the broad ends of the respective levers 248 and 250 in order to maintain positive pressure of the levers 248 and 250, against the fingers 256 and 258 at all times.

The two levers 248'and 250 are provided with inwardly directed protrusions 264 and 266 respectively extending crosswise diametrically adjacent the corresponding central openings 252 and 254 along lines parallel to the pivot axes, in order to press the respective stator leaves and rotor leaves of each section 222 and 224 into braking engagement. The opposite ends of the levers 248 and 250 are provided with opposed offset arms 268 and 210. A relatively stiff overload spring 212 is mounted between a recess 214 in the arm 268 and an adjusting cap nut 216 screwed into the housing member 202 in order to urge the front stator leaves 236 and the front rotor leaves 242 into frictional engagement by means of pressure exerted thereon by the protrusions 264 of the front lever 248. Likewise, a relatively weak override spring 262 is mounted between a recess 284 'in the other arm 210 and an adjusting cap nut 286 similarly screwed into the housing member 202 in'order to urge the rear stator leaves 226 and the rear rotor leaves 232 into frictional engagement by means of pressure exerted thereon by the protrusions 266 of the rear lever 250.

By maintaining the stator leaves 226 and 236 in frictional engagement with the respectiverotor leaves 232 and'242, the overload spring 212 "and the override spring 282 cooperate to maintain the position-adjusting mechanism 200 locked, in a predetermined condition. Disengagement of the stator leaves from the rotor leaves is effected by means of a flat lift cam 28'! located between the two arms 268 and 210 and rotatable there by means of an arm 288 which is controllable by suitable means including the Bowden wire 86. When the cam 281 is rotated to engage both arms 268 andflil, the protrusions 264 and266'are lifted or! the end stator leaves 226 and Z3B'tho1l by relieving the pressure between the stator leaves and the rotor-leaves, thus disengaging both sec!- tions 222 and 224 of the braking mechanism 23!}. While the braking mechanism 220 is thus 615th gaged, the posltiomadjusting mechanism 250 may be extended or compressed as desired by means of suitable thrusts applied to the red member 204. The stator leaves 228 and 236 may be made of stainless steel and the rotor leaves 232 and 2 of copper or any other suitable pair of nonegalle ing materials. The spacers 2135' and 245 may he "made of horn paper.

Normall the lift'cam 2Q! may he maintained in a neutral position'between the arms 26,8 and 21B merely byfloating therebetween or they may be maintained in a neutral position by means of 'atension spring 289 Which draws. the release arm 28!! forwardly into. engagement with a step pin 290 projecting outwardly from the side ofthe housin member 32.92. in either case, th opposite those 292 and 29s of the lift co 8? are spaced v ry sh rt distance rom ho'adjacent opposed faces of the arms 268 and all! .fo m e fro and re r eaos'i's nd 29h It is o he not d. that the Workin p r s o tho pos tion-adjustingechan sm a e a so enclosed "by-a dustmroof hou ing formed by the housing memb r 202, a forward tu ular cap member 295, and a rear tubular member 23'! bu that in th s case, the rod member 364 extends thr ugh and slides a ushin 9. at the r ar nd o he lat: ter tubular member 33 In practice, advanta is aken of the s ight amount of play or back-lash in ach of the bean ins assemblies 288 in. o der to ause the s ator loa es nd th io or le ves o de or rotate role v y to each ther when t ru f rce xc eding nredetonnined amoun s are app ied o the r member 204 in one direc ion or the othe More particularly, when a compr ssio rust s applied o the rod. m mber 266, h ot its is pr ssed forwardly in the ho sing member .202 a inst the force ex rted ther on. y th ov rl d sp ing 212 through the action of the front rak lover 348- As he ou 206 moves in t is ir ction, the width of the fr nt gap 295 rad a ly i c ea es and the width of the rear gap 234 graduall di inish s. Finally, the rear lever arm 21!; con,- tao s the rear f ce 293 o the l f am 2 her y reliev g the pres ure b twe n th friotioh lly ehgagedsta or leaves 226 and rotor leaves 232 of the rear ection 2.24 of t e b ake m a ism- This ac i n facilitate by provid n ui ciont back l sh in th front bearing ass mb y 20.8.-

In compressing th position adi s ing mo h nism 200, compression occurs after the pressure exerted by the overrid spirn 282. n the ro secti n 24 of he b ak m c anism 229 is r duced to zero. Thus, after the oa se tion comes comple lydi ons cdall the backlash in the front beari g a sembly 2% is then taken p and he not .105 rotates when the braking force e tablished by th overload sp ng 2 between t e front stator and the front rotor leaves 235 and 242 is overcome. The magn ude e min mum for e cguirod to produce such t io f th nut I96 depend part upon he m ch nical ad vantage of the threads of the rod member 2.04

and the nut 2136, the strength pi -the overload hrine 212, andtho ooeiiioient of friction of the engaging surfaces of the front section 222 of the braking mechan sm .220.- I

In aim lar manner. a larger and larg r X= tension thrusts are'app ied to he od mem er 20% i n the opposite. di ec i n commencin with he lift cam in its neutral position the width of the rear gap 2285 increases and the, width of the front gap 294 gradually diminishes until the front arm 268 engages the front face 292 of the lift cam 28? thereby relieving the pressure between the front stator leaves 236 and the front rotor leaves 242. Thereafter, the nut 206 becomes free to rotate when the extension thrust increases to a value onceeding the force which can be held by the override spring 282 acting alone considering the me.- chanical advantage of the threads and the coefllcient of friction of the rear stator and rotor leaves 232 and 235.

From the foregoing it is readily seen that by employing a relatively strong overload spring 212 and a relatively weak override spring 282, the positioneadjusting mechanism 200 is capable of remaining locked in a set position against compression forces less than a relatively high predetermined value established by the overload spring 212 and is capable of becoming unlocked against extension forces which exceed a relatively low value established by the strength of the override spring 282. Thus when the adjusting mechanism 200 is mounted on an airplane chair Ill in the manner hereinabove described, the chair is able to withstand relatively large rearwardl-y directed forces exerted against the back member but still is adapted to be raised readily when only relatively small forwardly directed forces are'applied thereto. 1

Form fr-The third form of position-adjusting mechanism illustrated in Figs. 12 to 17 inclusive also comprises a split housing member 302 and a threaded rod member 304 respectively connected between the front and rear cross-rods 22 and 34 of an airplane chair in the manner hereinbefore explained. The position-adjusting mechanism 390 also comprises a threaded nut 306 supported between front and rear ballebearing assemblies '30! and 308 along an axis extending longitudinally through a passage 3.09 within the housing member 300. The nut 306 is provided with an enlarged middle portion 310 of rectangular configuration providing a shoulder 3 at the front end thereof which firmly abuts the inner race 312 of the front ball-bearing assembly 387. A flange 3M is-formed on the nut 306 at the other end of the rectangular portion 3H] and intermediate the ends of the nut. A narrow tubular neck 3L6 extending rearwardly from the flange SM, is adapted to slide freely within the inner race 3l8 of the rear ball-bearing assembly 308.

An override spring 320 is mounted coaxially with the rod member 304 in compressed condition between the flange 3| 4 and a washer 322 which engages the inner race 3 l 8 of the rear ballbearing assembly 308. The override spring 329 acts to force the nut 306 into its most forward position between the wo bea assemblies it? and 308. The front bearing assembly 3b! is normally held, stationary within the housing member 302 n mly against a retainer ring 4 or ot r stop member mounted firmly on the housing member 2,

9 1h? ot e hand. the r r b i g assembly 308 i sli able th h sin member 302 and is adiustab y positi n e e y a me with th inne nd f a a justing tube 326 which is thrcadably mo able inwa dly an outwardly of the housin mem er &2 By so: Jus ine the pos tion of the tube 326 tho hots: ing memberv 3.02. it lspossible t vary heioroc exerted by th override spring .3 on the f ahs 314 of the nut 306 and thus to vary the maximum value of extension thrust against which the position-adjusting mechanism 300 may remain locked.

While the override spring 320 may be in the form of a helical spring, it is preferably in the form of two sets of Belleville washers arranged in opposing relationship, since such a sprin s an extremely high compliance per unit length. In other words, the ratio of compression force to distance compressed for such a spring is very high even though it is very compact.

A braking mechanism 330 is provided for preventing rotation of the nut 306 in the housing 302 so the position-adjusting mechanism 300 can be set in any desired position. The braking mechanism 330 comprises a group of stator discs, plates, or leaves 332 interleaved alternately with a group of rotor discs, plates,or leaves 334. The

two sets of leaves 332 and 334 are frictionally engageable in orderto prevent rotation of the nut 303 within the housing 302. The rotor leaves 334 are provided with central square apertures 336 which embrace the rectangular portion 310 of the nut B sufficiently closely to cause them to rotate with the nut'but at the same time permit them to slide axially thereon. The stator leaves 332 are provided with ears 338 on opposite sides thereof provided with slots 340 which embrace guide rods 342 and 344 firmly held within the 1 housing member 302 on opposite sides of the passage 309 therein. This arrangement prevents the stator leaves 334 from rotating within the housing member 302. but at the same time permits them to slide axially therein.

The braking mechanism 330 also includes a brake lever 343 comprising a pressure arm 345 and a cross-arm 346 arranged at right angles within the housing member 302. The pressure arm 345 lies cross-wise within the housing member 302 and is provided with a central aperture 343 which encircles the square portion 3l0 of the nut 306. The two ends of the pressure arm 345 are provided with passages 350 and 352 which encircle the guide rods 342 and 344. The passage 352 adjacent the connection of the pressure arm 345 to the cross-arm 346 encircles the corresponding rod 342 very loosely the two fingers 353 on opposite sides of the passage 352 projecting into slots 355 on opposite sides'of the crossarm 346. But the other passage 350 encircles the corresponding rod 344 closely but without binding. The pressure arm 345 is provided with protrusions 354 on opposite'sides of the opening 343 and along an axis perpendicular to the line between the holes 350 and 352; These protrusions serve to press the interleaved stator and rotor plates 332 and 334 together to lock the p0 sition-adjusting mechanism 300 in a set position.

The stator plates 332 'and the rotor plates 334 are made of any suitable pair of brake materials such as Phosphor bronze and low carbon steel.

The cross-arm 346 lies substantially parallel to the axis of the housing and adjacent one of the guide rods 342, extending rearwardly in the housing in a direction away from the trunnions 358. The cross-arm 346 includes a branch arm or finger 353 lying at right angles to the main portion thereof and extending radially outwardly from the center of the housing member. An

branch arm 356 and is compressed thereagainst by means of a plug 351 which is threadably ad- 345 at the protrusions 354, but the forward movement of the upper end of the pressure arm 345 is limited by means of a head 362 at the forward end of the upper guide rod 344. This head is arranged to be moved backward and forward slightly within the housing member 302 by means of an adjusting screw 364 having a tapered point which engages a tapered crown 356 on the head 362.

With this arrangement, the spring 360 exerts a force through the protrusions 354 to maintain the leaves 332 and 334 in braking engagement as long "as the force tending to compress the position-adjusting mechanism 300 lies below a predetermined overload value. This value is determined partly by the force exerted by this spring on the finger 356 and partly by the mechanical advantage of the threads and partlyby the coefficient of friction of the contacting surfaces of the leaves.

The brake release mechanism comprises a semi-cylindrical lift cam 333 which is rotatable about its axis within the housing into and out of engagement with the finger 353 by means of an external lever 310 which is controlled by means of the Bowden wire 86. While the brake mechanism 330 is engaged, a small gap 363 exists between the finger 356 and the flat face of the lift cam 363, so that the full force of the spring 360 on the leaves 332 and 334 may be obtained. To assure the existence of such a gap during brake engagement the crank arm 310 is normally urged against a. stop pin 312 by means of a tension spring 314. However, if desired, the pin 312 and spring 314 may be omitted permitting the cam to tilt against the finger 356 lightly without diminishing the braking force-of the overload spring 346 appreciably.

In order to disengage the brake mechanism 330 the lift cam 363 is turned, thereby engaging finger 356 pressing it against the spring 360. Due to the loose fit of the hole 350 with the guide rod 344, the pressure arm 345 is pivoted on the rod 344 as the finger 356 is pressed against the spring 360. This action relieves the pressure of the protrusions 354 on the leaves 332 and 334, thus disengaging the braking mechanism and permitting the rod 304 to be moved in either direction through the housing member 302, by means of a small force applied in either direction to the back member l6 of the chair. When the lift cam 368 is returned to its normal position, the spring 360 forces the protrusions 354 against the leaves 332 and 334 again thereby engaging the brake mechanism 330 and locking the position-adjusting mechanism 300 in the desired position.

If, while the braking mechanism 330 is engaged, a compression thrust is exerted against the rod member 304, the nut 306 is moved slightly forwardly within the housing member 302 by virtue of the play or back-lash in the front hear ing assembly 301, thereby slightly increasing the compression of the leaves 332 and 334 between the flange 314 and the pressure arm 345.

In view of the fact that the compression spring 360 exerts a very small force compared to the thrust in question, the leaves 332 and 334 are not compressed substantially but merely shift forwardly within the housing member 302 causing the pressure arm 345 to pivot slightly maintaining the full force of the spring 360 thereon.

Thereafter as the compression thrust increases, the resultant turning moment exerted by the threads of the rod member 304 onthe nut 306 increases until it equals the frictional rr'etarding force exerted between the two sets of frictionally engaged leaves by the overload spring 365-. Further increase of thrust causes the nut 35% to rotate, permitting the position-adjusting mechanism to compress. 'The value of compression force at which such compression occurs depends upon the coefiicient of friction ofthe fr'ictionally engaged surfaces of the leaves 332 and 336. For this reason the strength of the overload spring 332 is adjusted by means of the plug 351 to permit the position-adjusting mechanism 305 to hold a given maximumload even when the coeflilcient of friction is at the smallest value that may be attained through wear of the leaves or in any other way.

Now if an extension thrust is exerted on the rod member 364, the neck 3H3 slides within the inner race 3 it of the rear bearing assembly compressing the override spring 326, and the nut 306'is drawn rearwardlywithin the housing member 3132. During the initial portion of this move-' ment, corresponding to small extension thrusts, the pressure arm 35 2 pivots, reducing the Width of the gap between the finger 35B and the lift cam 368. Finally, when the fingerttii enga es the lift cam 36%, further increase of extension thrust increases the pressure of the finger 356 on the lift cam 368 relievingthe pressure between the stator and rotor leaves 332 and 33$. -As the force of the finger 353 on the lift earn 368 increases the force exerted by the protrusions 354 on the leaves 332 and 334 decreases, thereby reducing the'braking force tendingto prevent rotation of the nut 3QS.- When the turning moment exertedon the nut 36% by the extension force exceeds the braking moment exerted by the frictional forces between the two sets of leaves 332 and 33 3, the nut 3B6 commences to rotate.

If a large extension thrust is appliedsuddenly, the stator leaves 332 and the rotor leaves 334 become completely disengaged, permitting the nut 336 to accelerate-rapidly. However, in the normal course of events, the nut 306 accelerates to the point where its speed of rotation corresponds to the speed of extensionof the position-adjusting mechanism 390 causing the stator leaves 33$ and'the'rotor 1eaves332 to engage-slightly, and thereby govern the frictional force therebetween in accordance With the amount required to permit extension. Thus, it is seen that while the extension thrust applied exceeds the threshold amount mentioned required to relieve the pressure between the leaves at a constant speed, the leaves remain interengaged and the frictional force therebetween is governed automaticallyto correspond with the speed of extension of the position-adjusting mechanism 3%.

This form of position-adjusting mechanism acts. very similar to form 1 described hereinabove, in that the minimum value of the extensionforce required to cause extension is practically independent of the coefficient of .frictionof the braking surfaces. In this case, Equation .2 alsov applies where FE the residual braking force, is the force exerted by the protrusions 35% upon the leaves 332 and 334. In this .case,..the constant of proportionality. K; depends on (a) the binding'angle, (-b) the pitch. angle,..(c) the radius of the threads, and (d) the effective mean radius atwhich the force between the'leaves is applied. In thiscase, also, if. the coefficient of :frictionp changes for some reason, only aslight change-in .the :extension force, is required to adjust the .residualbraking force exerted-bythe .protrusions 18 354 to a sufiiciently 10w value- 'to permit extension of the position-adjusting mechanism 360.

It is to be noted that in this form of the invention, also, the main working parts of the braking mechanism 332 are enclosed within a dust-proofhcu'sing formed by the housing memextension and compression of the position-adjusting mechanism a small annular gap 382 exists" between the rod member 3il4 and a ferrule 38d mounted at theouter ends of the tube 326 and the nut Slit is-properly aligned with the rod member 33% by means of the self-aligning ball bearing assemblies 308. A spacer sleeve 386 of selected length encloses therod member 354 between the ferrule-tthi and the connector 388 at the rear end of the rodmember. The spacer sleeve 386' is employed to limit the compression of the position-adjusting mechanism, thereby limiting the maximum angle to which the back member 12 of the chair H] can be lowered,- or tilted rearwardly. Ina similar manner a tubular member 396 extends forwardly fromthe holdingring 324 to engage the head 392 of the cap screw 394 at the forward end of the rod member 306 in order to determine the minimum angle to which the back member l'2- may be raised, or tilted forwardly; A compression spring 396-is arranged concentrically with the sleeve 386- between the ferrule 38dand the connector 388. 'In order to facilitate the returnof the back member l2 of the chair to its'most upright position when the braking mechanism 33B is released by manipulation ofthe Bowden wire 86. It is to be noted that in the most upright position, the Sylphon bellows 389 is collapsed within an annular space 398 surrounding the tubular member 390 at the forward end of the housing member 302. I v I PART III cantingv type A fourth form of position-adjusting-mechamsm lililemploying the principles of thisinvention is illustrated in Figs. 18- to 22 inclusive. This form of the inventiondoes-not employ threads but merely a smooth rod and canting leaves which frictionally' engageand' remain engaged as long as" the compression and extensionloads lie belowcorresponding predetermined limits.

The position-adjusting mechanism Mil includes a bodymember QEl'Z'and a rod member tllsl which arerespectively connected-to the two cross-rods 22 and 34 of the airplane-chair it in the manner describedhereinabove. The position adjusting mechanism ittincludes a braking mechanismdiifi which is self-energizing and which comprises a plurality of canting washers vor leaves dill including front, middle, and rear canting leaves 4:! tot, 4 ilb, and ii i tcrespectively, all having. centralopeningsx -liif, the walls of which frictionally engage the cylindrical surface did of the rods member 48 3. noted that in this instance, the surface did of the rodimember rdtdlacts as .one of the .frictionally engageable brake: elements. In this case, an overload spring 415 is employed which .coopcrates with other elements .to determine the maximum load against-which the braking mechanism holds against compression thrusts. Also in this case, an override spring #3 I58 -:is employed to determine. the: threshold .above which the It is to be .brake mechanism 408 is released by extension thrusts.

The body member 402 is of flat, elongated, rectangular configuration and is provided with a longitudinal passage 420 in which the rod member 404 slides and a transverse rectangular passage 422 in which the'canting leaves 4I0 are located. A sliding cam bolt 424 is arranged to slide longitudinally within the body member 402 inorder to release the braking mechanism 408 to permit either compression or extension of the position-adjusting mechanism 400 by means of small thrusts applied in either direction. The cam bolt 424 is provided with a fiat inner side 426 and a rounded outer side 421 and the passage 428 within which it is arranged, is of similar cross-section in order to facilitate the guiding of the cam bolt backward and forward within the body member 402.

The actual movement of the cam bolt 424 and hence release of braking mechanism 408 is accomplished by means of a crank rod 430 which slides within a transverse slot 432 in the cam bolt 424. The crank rod 430 is connected between a crank hub 434- and a crank pin 436 which are rotatable within apertures in the body member 402 on opposite sides of the passage 428 behind the rectangular opening 422. The movement of the crank rod 430 is controlled by means of a lever 438 firmly secured to the crank rod 434. The lever 438 is movable about a pivot point established by a pin 440 projecting from the hub 434. Normally the lever 438 is urged into its rearmost position against a stop pin 442 at the upper end of the body member 402 by means of a compression coil spring 444 attached to the lower end of the lever and to a post 446 projecting from the body member. The lever 438 is moved to its forward position against the force of the spring 444 by means of the Bowden wire 86. The guiding of the cam bolt 424 within the passage 428 is facilitated by extending the cam bolt in the passage 428 on opposite sides of the rectangular passage 422.

The cam bolt 424 is provided with an enlarged slot 448 on the inner side thereof arranged in embracing relationship with the canting leaves 4"]. The rear face 450 of the slot 448 is straight, while the forward face 452 is inclined in the same direction as the canting leaves 4l0, being inclined with respect to the axis a:x of the position-adjusting mechanism a little more than the canting leaves. The upper ends of the leaves 4I0 are provided with slots 464 embracing the adjacent portion of the crown 421 of the cam bolt in order to prevent rotation of the leaves 4I0 within the body member 402.

A first, or snubber, pin 454 projecting through a passage 456 passing through the front face 452 is normally urged into engagement with the upper end of the front canting leaf 410a by means of a spring 451 compressed between a collar 458 on the pin and a threaded plug 460 which is adjustably movable inwardly and outwardly of the body member 402 in a threaded opening 462 at the forward end of the passage 428.

The overload spring 416 is arranged between a countersunk apertured threaded plug 4H and a threaded collar 412 within a cylindrical cavity 414 at the front lower end of the body-member 402. A threaded tubular member 416 extends forwardly from the threaded collar 412 and cooperates therewith to hold a second, or tripping, threaded pin 418 in any desired position therein,

the outer end of the tubular member 416. being slotted and pressed together slightly for this purpose. The tripping pin 418 carries a rounded tripping point, or tip, 419 at its inner end which is adjustable inwardly and outwardly of the rectangular aperture 422 in spaced relation with the lower end of the front canting leaf 4l0a. The tripping point 419 is forced by the overload spring 4l6 into its innermost position as determined by the shoulder 484 against which the collar 412 is forced. It is to be noted that the pin 418 and the tubular member 418 may be moved together as a unit through the central aperture of the adjusting nut M1.

The override spring M8 is also arranged between an apertured threaded plug 490 and a threaded collar 492 within a cylindrical cavity 494 at the rear lower end of the body member 402. A threaded tubular member 495 extends forwardly from the threaded collar 492 and cooperates therewith to hold a third, or holding,

pin 498 in any desired position therein, the outer end of the tubular member 496 also being slotted and pressed together slightly for this purpose. The holding pin 498 also carries a rounded tripping point 499 at its inner end which is adjustable inwardly and outwardly of the rectangular aperture 422 in spaced relation with the lower end of the rear canting leaf M00. The override spring 4l8 forces the tripping point 499 into its most innermost position as determined by the shoulder 491 against which the collar 412 is forced. The forward portion of the third, or holding pin 498 is encircled by a helical follower spring 500, which is arranged between the collar 492 and a recess 502 in the rear face of the rear canting leaf 0. In practice, the second and third pins 418 and 498 are aligned in opposing relation on opposite sides of the leaves 410 and the cylindrical cavities 414 and 494 in which they are arranged and formed axially in opposite ends of the body member 402 on the opposite side of the shaft 404 from the cam-bolt passage 428.

In operation, when the cam bolt 424 is in its rearmost or withdrawn position, the snubber spring 451 and the follower spring 500 urge the upper and lower ends respectively of the canting leaves 4!!) in opposite directions, the upper ends being urged rearwardly and the lower ends being urged forwardly causing the braking surfaces 2 of the apertures in the leaves M0 to frictionally engage the surface 4l4 of the rod member 404. While these braking surfaces are so engaged, the rod member 404 is locked against sliding movement within the body member 402 in either direction.

However, when the braking mechanism 408 is released by forward movement of the Bowden wire 86, the rear face 450 of the cam bolt-slot 448 engages the upper end of the rearmost canting leaf 4l0c. As the cam bolt 424 is pressed forward against the force of the snubber spring 451, the follower spring 500 presses the lower end of the leaves forward as a unit until the front leaf 4l0a contacts the tripping pin 418. At this time, further movement of the cam bolt causes the grip of the leaves 410 on the surface 4 of the rod member 404 becomes completely relieved.

While the brake mechanism is thus disengaged, the rod member 404 may be slid in either direction in the central passage 420 through the body member 402 to set it in a new position. As the cam bolt 424 is returned to its rearmost posi- 21' tion, theleaves filflfollowas a. unit by. virtue of the action-of the snubber spring. 4.58 andthe follower spring 580. When the rearleaf Milo contacts the holding pin sea, the leaves cant and finally disengage the rear shoulder 45!! of the cam bolt 424. When this occurs thesnubber pin 554 and the holding pin 698. hold the leaves Mil infrictional engagement with the rod member 494, thus locking theposition-adjusting mechanism 400 in the position in which it has been set.

With the braking mechanism 488 engaged, as compression thrusts are applied to therod memher 464, initially the leaves Alt are carried forwardly against the force exerted thereon by the snubber spring 557 until. they engage the forward face 652 of the slot Q48 in the cam bolt 42d. Further forward. movement of the upper end of the canting leaves 2-18 is precluded at that time. Thereafter as the thrust. of the rodmember. 6% increases in the same direction, the leaves dill deflect, pressing their braking surfaces M2. with more and more force against the braking surface AM of rod member 365., After a little deflection, the front canting leaf llila engages the tripping pin 4'39 urging it forwardly against the force of the overload spring M5. The force exerted by the leaves M3 on the rod increases as the thrust increases for a while. But further increases in the gripping force is resisted more and more by the overload spring M3, until finally this force is relieved reducing the frictional force along the surfaces M2 and 6M. As the thrust continues to increase in the same direction, it finally exceeds the value of thrust which can be held by the frictional force. At this time, the brake mechanism is released permitting the rod memberAM to slide through the canting leaves in continuous frictional engagement therewith. During this sliding movement, the axially directed frictional force exerted by the canting leaves Mil on the rod member tilt is governed in part by the force exerted by the overload spring Mt when compressed and in part by the coefficient of friction between the braking surfaces. I

With the braking mechanism 688 engaged, as extension thrusts'are applied to the rod member 404, initially the leaves Kilt are carried rearwardly against the force exerted thereon by the third pin $98. After the collar 492 is lifted off. the shoulder 49?, the gap between the rear face 658 of the slot M8 in the cam bolt'424 and the gap between thepin 438 and the front'surfaceof the slot 532 are takenup, causing the rear leaf Milo to engage the shoulder 45!} firmly. Thereafter as the thrust on the rod member MM increases in the same direction, the shoulder 53 exerts'an increasing force on the leaves in opposition to the force of the snubber spring 53, andthe force of the override spring did. Thereafter, the force exerted between the braking sur-v faces 3V.) and M4 decreases until it reaches a value too small to hold againstv the extension force by virtue of the friction between the braking surfaces.

brakingfsurfaces All and 414 dry, that is, un

lubricated. In practice,-. a value. of Mi-equal to about 5 has been. found. to be. verysatisfactoryi With. smooth braking surfaces the value of -,u and hence ,uM changes very slightlyand sincethepere centage change of release load is Verymuch smaller than the percentage.changeofs the minimum force required to extend the position! adjusting mechanism lilll isv practically inde-: pendent of the coefiicient of friction.

In order .to provide a braking mechanism. 4538 having long. life and uniform characteristics, fiat sections are formed in each. of the... leaves H6 at the edge thereof which contacts therod member til-i as. illustrated in Fig. 22. These fiat sections are actually formed by placing each of the leaves on a. cylindrical die and then ti1t-. in each of the leaves. with a strongccouplei in order to crush two diagonally opposite edges. The crushed edges arethendeburred, rounded, polished, and then burnished oilj Preferably, the fiat sections 5! extend. inwardlyofthe apertures in the'leaves Mfitoadistanceequal to about to /2 of the thickness of a leaf. In this way, braking surfaces are formed in. the leaves which bear uponthe surface 4 M of the rod member @0 3 over a relatively large area and thus minimize indentation and resultant wear of the cylindrical surface 4M. In order to further pro-.- vide a braking mechanism 498 of longlife, the leaves i H] are preferably composed of hardrolled beryllium-copper alloy Brylco 25, 2 B and S gages hard and the finishedleaves. are. heat treated in order to raise their tensilestrength to a high value. Also, the rod member Midis composed of SAE 4130 chrom-molybdenum steel which has been treated to render its tensile strength at least 209,000 p. s. i. Both the frictionally engageable surfaces of the canting leaves 4H] andthe-rod member 464 are finished to an uniformity of 5 micro-inch or better.

The presence of such flat sections draws the eifective pressure point inwardly from the outer sides of the respective leaves 4E0, thereby. increasing the mechanical advantage M of the leaves when they are considered as levers for the transmission of forces to the surface GM of the rod member 4M from any of the pins 456 416, and 699. This increase in mechanical advantage is achieved without, however, sacrificing the strength of the leaves MD as would occunif their thickness were reduced.

It is to be noted that the follower spring 500 and the snubber spring 557 cooperate to maintain the canting leaves am in frictional engagement with the rod member 38% even though the braking surfaces N2 of the canting leavessbecome worn. Even though wear results in reducing the mechanical advantage M, the minimum force required for extension remains substantially unchanged.

From the foregoing it is readily seen that this position-adjusting mechanism is also capable of remaining locked against a wide range of'forces exerted in one direction there-on but is capable of being readily adjusted by relatively small forces exerted in the opposite direction.

PART IV Rsum Two main types of the invention have, been described hereinabove.

tion-adjusting mechanism setina predetermined ployed to permit the braking surfaces to slip in one direction or the other only when the thrust between the body member and the rod member in the corresponding direction exceeds a predetermined amount. These two predetermined amounts are made unequal so that the positionadjusting mechanism is capable of holding against large forces applied in one direction and against only small forces applied in the other. Such a position-adjusting mechanism finds particular utility when installed on a chair having a tiltable back member which is designed to hold against relatively large backward-tilting forces but which is designed to be raised easily by means of relatively small forward-tilting forces. In all forms of the invention, a brake release mechanism is employed for urging gap-defining elements together to relieve the pressure existing between the frictionally engageable braking surfaces in order to release their hold on the rod member so that the rod member may be moved relatively to the body member by means of very small forces applied in either direction.

In three forms of the invention, namely, forms 1 and 2 of the screw type, and the single form of the canting type illustrated, a preloaded spring and a pair of gap-defining elements are employed to prevent slippage of the frictionally engageable braking surfaces while the thrust tending to produce slippage lies beneath a predetermined value. Furthermore, the gap-defining elements are arranged to engage when the thrust attains the predetermined value mentioned and acts to relieve the pressure between the frictionally engageable braking surfaces in such a way as to maintain the frictional resisting force (which is parallel to the braking surfaces) substantially constant during slippage. In these three forms of the invention, the force exerted between the gap-defining elements during slippage varies as an inverse function of the coefficient of friction a existing between the braking surface. In this way, the frictional force is maintained substantially constant during slippage and independent of the coefficient of friction at least over the very wide range of values of the coefficient of friction likely to be encountered in practice.

The gap-defining elements which operate in these three forms of the invention to relieve the force exerted by the override spring are usually in the form of two solid elements, one of which is mounted firmly on the body member and the other of which is carried with a brake member. It is to be noted that the variation in force that occurs between these elements between the time that they first make contact and the time when the braking surfaces would become completely disengaged, causes them to be compressed. The compression is very slight because of their high compliance. However, it is not necessary for these elements to be solid, but they may be in a form involving the action of other spring means having a higher compliance than the override spring during brake release so that the force between these points may change rapidly though 24 the parts without departingfrom the principles of the invention. Reference is, therefore, to be had to the appended claims for a definition of the limits of the invention.

The invention claimed is:

1. In an adjustable chair comprising a support member and a tiltable back member, the improvement which comprises: an adjustable positioning mechanism comprising a body member and a rod member connected between said support member and said back member. for setting said back member in a predetermined tilt position, said adjustable mechanism comprising a brake mechanism having first and second brake means interconnecting said body member and said rod member, said brake means having frictionally engageable braking surfaces adapted when engaged to oppose relative movement of said members, means for maintaining said braking surfaces engaged to hold said back member against relatively large rearward-tilting forces, a preloaded spring opposing forward-tilting forces and arranged to urge said braking surfaces into engagement to produce a frictional force along said surfaces which resists relative movement of said members by forward-tilting forces, and means including a pair of elements engageable during relative movement of said members for relieving the force urging said braking surfaces together whereby the minimum value of forward-tilting forces required to tilt said back member forward while said brake mechanism is operative is maintained at a substantially constant relatively low value irrespective of variations in the coefficient of friction between said surfaces.

2. In an adjustable chair comprising a support member and a tiltable back member, the improvement which comprises: an adjustable positioning mechanism comprising a body member and a rod member connected between said support member and said back member for setting said back member in a predetermined tilt position, said adjustable positioning mechanism comprising a brake mechanism having first and second brake means interconnecting said body member and said rod member, said brake means having frictionally engageable braking surfaces, means for maintaining said braking surfaces engaged to hold said back member set in a predetermined position against relatively large rearward-tilting forces, means including a preloaded spring for urging said braking surfaces together to resist forward-tilting forces, and a pair of elements engageable in response to forward-tilting forces exceeding a predetermined relatively low value for relieving the force urging said braking surfaces together, whereby said back member is tilted forwardly by forward-tilting forces exceeding said predetermined low value.

3. In an adjustable chair as defined in claim 1, means for adjusting the preloading force exerted by said spring to vary the predetermined low value of forward-tilting force required to relieve the force urging said braking surfaces together.

4. In an adjustable chair as defined in claim 2, brake release means controllable by a chair occupant for bringing said elements into engagement irrespective of such tilting force for disengaging said braking surfaces, whereby free relative movement of said chair members is permitted.

5. In an adjustable chair comprising a support member and a tiltable back member, the improvement which comprises: an adjustable positioning mechanism comprising a body member and a rod member connected between said supportmember and said back member for settingsaid back member'in'apredetermined tilt position, said adjustable positioning mechanism comprising a brake mechanismhaving first and second brake means respectively associated with said body member and said rod. member, said brake means having frictionally engageable braking surfaces, means manually controllable by an occupant of the chair for disengaging said braking surfaces to permit tilting said back member in either direction by relatively small forces appliedthereto,-means for maintaining. said braking surfaces engaged to hold said back member set in a predetermined position against relatively large rearward-tilting forces, means including a preloaded spring for urgingsaid braking surfaces together to resist forward-tilting forces, and a pair of elements engageable in response to forward-tilting forces exceedinga predetermined value for relieving the force urging said, braking surfaces together, whereby said back member is tilted forwardly by forward-tilting forces exceeding said predetermined value.

6. In an adjustable chair as defined in claim 5, means for adjusting the preloading force exerted by said spring to vary the predetermined low value of forward-tilting force required to relieve the force urging said braking surfaces together.

7. In an adjustable chair comprising a support member anda tiltable back member, the improvement which comprises: an adjustable positioning mechanism ccim'p'rising'a body member and a rod member connected between said support member and said back'member for setting said back member in a predetermined tilt position, said adjustable'positioning mechanism comprising a brake mechanism having first and second brake means respectively associated with said bod member and said rod member, said brake means having frictionally engageable braking surfaces, means including a first preloaded spring for urging said braking surfaces together to resist forward-tilting forces, a first pair of elements engageable in response to said forward-tilting forces exceeding a predetermined relatively low value for relieving the force urging said braking surfaces together, whereby said back member is tilted forwardly by forward-tilting forces exceeding said predetermined low value, means including a second preloaded spring for urging said braking surfaces together to resist backward-tilting forces, and a second pair of elements engageable in response to rearward-tilting forces exceeding a predeter mine'd'relati'v'ely high value for relieving the force urging said braking surfaces together, whereby said back member is tilted rearwardly by rearward-tilting forces exceeding said predetermined high value. V

"8'. In an adjustable chair as defined in claim '7, means for adjusting the preloading forces exerted by said first spring to vary said predetermined low value of forward-tilting force, and means for adjusting the 'prelo'ading force exerted by said second spring to vary said predetermined high value of backward-tilting force.

9. In an adjustable chair including two chair members, namely a support member and a tiltable back member and also including a positionadjusting mechanism and employing a pairrof complementarily threaded members respectively mounted on said chair members, one of said threaded members being rotatably sup-ported relative to theother threaded member to permit relative movement of said two threaded membars when an axial thrust is applied therebetween whereby said back member is'movable from one tilted position to another, the improvement which comprises: a brakernechanism including 'frictionally engageable stator and rotor brake means for holding said back member set in a predetermined position, said rotor brake means being carried by said rotatable threaded member, first and second springs for urging said two brake means into engagement to resist rotation of said rotatable threaded member, said first spring acting to prevent slippage between said stator and rotor brake means while. said backward tilting forces are less than'a relatively large overload value. said second spring acting in opposition to forward-tilting forces, and means including a pair of elements engageable when said second spring is compressed more than a predetermined amount by forward-tilting forces for relieving the force urging said brake means together whereby said brake mechanism is released to permit rotation of said nut when said forward-tilting force exceeds a corresponding relatively low predetermined value.

10. An adjustable chair as defined in claim 9 including means controllable by the chair occupant for urging said springs apart to disengage said two brake means.

11. In an adjustable chair comprising a support member, and a ytiltable back member, the improvement which comprises: an adjustable positioning device comprising a body member and arod member interconnecting said support member and said back member for holding said backmember set in av predetermined tilt position, said adjustablepositioning device comprising a brake mechanism including canting means having apertured walls frictionally engageable with the'surface of said rod member, means including a first preloaded spring for urging said walls against said surface to resist forward-tubing forces, a first element engageable with one 'endof said canting means in response to forward-tilting forces exceeding a predetermined o relatively low value for relieving the force urging said walls against said surface, whereby said back member is tilted forwardly by forward-tilting forces exceeding said predetermined low value, means including a second preloaded spring for urging said walls against/said surface to resist backward-tilting forces, and a second element engageable with the opposite end of said 'ca'n'ting means in response to rearward-tilting forces exceeding a predetermined relatively high value forrelieving the force urging said walls against said surface, whereby said back member is tilted rearwardly by "rearward-tilting forces exceeding a predetermined relatively high value.

12. An adjustable chairas defined in claim 1'1 comprisingmeans controllable by the chair oc-' cupant for forcing 'said elements in opposite directions 'against'said'canting means to disengage s'aid walls from said surface, whereby said can: member is easily tilted in either direction.

'13. In an adjustable structure including two relativelymovable structural members, the improvement which comprises a position adjusting mechanism including a body member and a rod member interconnecting said structural members, said body member and said rodmember being mutually movable in opposite 'direction s to various relative positionsin an extended range in, response to forces applied. in corresponding opposite directions between said structural members, the improvement which comprises: a brake mechanism including brake means interconnecting said body member and said rod member,

said brake means having frictionally engageable braking surfaces that are mutually slidable, first and second springs for urging said braking surfaces into engagement to resist relative movement of said structural members at various positions in said range, said first spring acting to permit sliding movement between said braking surfaces only while the forces acting to move said structural members in one direction exceed a relatively large predetermined value, said second spring acting in opposition to a force acting to move said structural members in the opposite direction, and means including a pair of relatively movable elements normally unengaged when said second spring is compressed less than a predetermined amount and becoming engaged when said second spring is compressed more than a predetermined amount by a force applied in said opposite direction for relieving the force urging said braking surfaces together whereby said brake mechanism is released to permit sliding movement of said braking surfaces only when said latter force exceeds a relatively low predetermined value.

14. An adjustable structure as defined in claim 13 including manually controllable means operative to urge said springs apart to disengage said two braking surfaces at any part of said range.

15. In an adjustable structure including two structural members arranged for relative movement by forces applied therebetween, the improvement which comprises: an adjustable positioning device comprising a body member and a rod member interconnecting said structural members for setting said structural members in predetermined relative positions, said adjustable positioning device comprising a brake mechanism including canting means having apertured walls frictionally engageable with the surface of said rod member, means including a preloaded spring for urging said walls against said surface to resist relative movement of said structural members in one direction, a first element engageable with one end of said canting means in response to such forces applied in said one direction and exceeding a first predetermined value for relieving the force urging said walls against said surface, whereby said structural members are moved in said one direction by forces exceeding said first predetermined value, and a second element engageable with the opposite end of said canting means in response to forces applied in said opposite direction, means including a second preloaded spring acting on said second element for relieving the force urging said walls against said surface, whereby said structural members are free to move in said opposite direction by forces exceeding second predetermined value.

16. An adjustable structure as defined in claim 15 including manually controllable means including a lever for effecting relative movement of said elements and comprising means including a third spring connected to said lever for urging said elements apart and away from said canting means.

1'7. An adjustable structure as defined in claim 15 wherein said elements are located on opposite sides of said canting means and are spaced from said canting means when no force is applied between said structural members, and means for adjusting the relative positions of said elements in the direction parallel to the axis of said rod.

18. An adjustable structure as described in claim 15 including auxiliary springs urging said ends toward the respective elements for 28 4 taining said walls in engagement with the surface of said rod member.

19. In a position-adjusting mechanism including a body member and a rod member which are mutually movable over an extended range by a thrust a plied therebetween in a predetermined direction, the improvement which comprises: a brake mechanism comprising first and second brake means interconnecting said body member and said rod member, said brake means having braking surfaces adapted to be slidably engaged throughout said range and adapted when engaged to frictionally oppose relative movement of said members in said direction at any part of said range, apreloaded spring opposing such thrust and arranged to urge said braking surfaces into engagement throughout said range to produce a frictional force along said surfaces which resists relative movement of said members by such thrust, and means including a pair of normally unengaged elements engageable during relative movement of said members for re lieving the force exerted by said preloaded spr n in urging said braking surfaces into engagement, whereby said frictional force is maintained substantially constant irrespective of variations in the coefficient of friction between said surfaces.

20. In a position-adjusting mechanism including a body member and a rod member which are mutually movable over an extended range, the improvement which comprises: a brake mecha nism comprising first and second brake means respectively associated with said body member and said 'rod member, said brake means having braking surfaces adapted to be slidably engaged throughout said range and adapted when engaged to frictionally oppose relative movement of said members at any part of said range, means including a preloaded spring opposing thrust applied in a predetermined direction between said body member and said rod member, said means urging said braking surfaces into engagement while such thrust is applied at any part of said range, and means including a pair of relatively movable elements that are normally unengagedwith each other but are engageable in response to such thrust in excess of a predetermined value for relieving the force urging said braking surfaces into engagement whereby said rod member moves relative to said body member.

21. A position-adjusting mechanism as defined in claim 20 comprising means including an adjustable element engaging said spring for adjusting the preloading force exerted by said spring to vary the predetermined value of thrust required to move said rod member relative to said body member from one relative position to another in said range.

22. A position-adjusting mechanism as defined in claim 21 in which said elements are spaced apart to define a small gap when no thrust is applied between said members, and comprising means for moving one of said elements while said body member and rod member are in a fixed relative position for adjusting the size of said ap.

23. A position-adjusting mechanism as defined in claim 20 comprising: brake release means for forcing said elements into engagement irrespective of such thrust for disengaging said braking surfaces, whereby free relative movement of said. members is permitted.

24. In a position-adjusting mechanism, the combination which comprises: a body member and a rod member which are mutually movable.

over an extended range, a brake mechanism. 

